You can always search online for the Left and Right Ambient Light Sensors, then search for a compatible keyboard - bear in mind the current MacBookPro keyboard will not work with the older logicboards, the interface is completely different!
Provided your PowerBook is of the 15 or 17 Alu flavour,
installing them shouldn't be too much hassle, cause there's connectors one the logic-board already! Good luck.
NB, the PowerBook 12" never ever had Backlight Keyboard as a optional extra.